To satisfy this requirement, energy dissipators in which movement between the parts of the structure as a result of an earthquake is resisted by steel elements which undergo considerable deformation when their yield stress is exceeded are known and used extensively.
Owing to the magnitude of the deformations undergone, the behaviour of these elements leaves the elastic range and enters the plastic range, giving rise to energy dissipation.
Once installed, these energy dissipators have the disadvantage, in use, of behaviour which is often far-removed from the expected behaviour. Moreover, their behaviour is not repeated identically with repeated earthquakes but deteriorates gradually until it is wholly inadequate.
Energy dissipators substantially of the hydraulic shock-absorber type have been proposed. These dissipators cannot be left installed for years and years with confidence that they will function as they should when required. On the contrary, they require onerous periodic maintenance operations to replace seals and to top up the oil or to replace them with new improved dissipators, with all of the problems which accompany such operations.
The problem upon which the present invention is based is that of devising an energy dissipator of the type specified which has structural and functional characteristics such as to overcome the disadvantages mentioned above with reference to the dissipators of the prior art.